学习目标
学习openGuass数据库中如何对表进行修改
课程学习
1.测试准备
--首先创建一张测试表。
drop table if exists test;
create table test(
id bigint,
name varchar(50) not null,
age int default 20,
primary key(id)
);
2.为表添加字段
--查看表test的信息
\d test
--为表test新增一列，列名为sex，数据类型为Boolean：
alter table test add column sex Boolean;
--执行下面gsql命令，查看表test的信息
\d test
3.删除表中的已有字段
--执行下面的SQL语句，删除刚刚添加的列sex：
alter table test drop column sex ;
--执行下面gsql命令，再次查看表test的信息
\d test
- 删除表的已有约束
--表test上有一个名叫test_pkey的PRIMARY KEY约束。执行下面的SQL语句，删除这个约束：
alter table test drop constraint test_pkey;
--执行下面的gsql命令，再次查看表test的信息：
\d test
--或直接查看约束是否被删除
select * from pg_constraint where conname like 'test_pkey';
5.为表添加约束
--执行下面的SQL命令，为表test添加刚刚删除的主键约束：
alter table test add constraint test_pkey primary key(id);
--再次查看表test的信息：
select * from pg_constraint where conname like 'test_pkey';
\d test
6.修改表字段的默认值
--执行下面的SQL语句，将age的默认值变更为25
alter table test alter column age set default 25;
\d test
7.修改表字段的数据类型
alter table test ALTER COLUMN age TYPE bigint;
\d test
8.修改表字段的名字
ALTER TABLE test RENAME COLUMN age TO stuage;
\d test
9.修改表的名字
--修改表的名字。执行下面的SQL语句，将表test的名字变更为mytest：
ALTER TABLE test RENAME TO mytest;
\d mytest
10.删除表
DROP TABLE mytest;
课程作业
1.创建表，为表添加字段
root@modb:~# su - omm
omm@modb:~$ gsql -r
gsql ((openGauss 3.0.0 build 02c14696) compiled at 2022-04-01 18:12:00 commit 0 last mr )
Non-SSL connection (SSL connection is recommended when requiring high-security)
Type "help" for help.
omm=# create table test(
omm(# id bigint,
omm(# name varchar(50) not null,
omm(# age int default 20,
omm(# primary key(id)
omm(# );
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "test_pkey" for table "test"
CREATE TABLE
omm=# \d test
Table "public.test"
Column | Type | Modifiers
--------+-----------------------+------------
id | bigint | not null
name | character varying(50) | not null
age | integer | default 20
Indexes:
"test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default
omm=# alter table test add column sex Boolean;
ALTER TABLE
omm=# \d test
Table "public.test"
Column | Type | Modifiers
--------+-----------------------+------------
id | bigint | not null
name | character varying(50) | not null
age | integer | default 20
sex | boolean |
Indexes:
"test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default
omm=# 
2.删除表中的已有字段
omm=# \d test
Table "public.test"
Column | Type | Modifiers
--------+-----------------------+------------
id | bigint | not null
name | character varying(50) | not null
age | integer | default 20
sex | boolean |
Indexes:
"test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default
omm=# alter table test drop column sex ;
ALTER TABLE
omm=# \d test
Table "public.test"
Column | Type | Modifiers
--------+-----------------------+------------
id | bigint | not null
name | character varying(50) | not null
age | integer | default 20
Indexes:
"test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default
omm=# 
3.删除表的已有约束、添加约束
omm=# \d test
Table "public.test"
Column | Type | Modifiers
--------+-----------------------+------------
id | bigint | not null
name | character varying(50) | not null
age | integer | default 20
Indexes:
"test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default
omm=# alter table test drop constraint test_pkey;
ALTER TABLE
omm=# \d test
Table "public.test"
Column | Type | Modifiers
--------+-----------------------+------------
id | bigint | not null
name | character varying(50) | not null
age | integer | default 20
omm=# select * from pg_constraint where conname like 'test_pkey';
---------+--------------+---------+---------------+-------------+--------------+----------+----------+----------+-----------+-------------+-------------+-
--------------+------------+-------------+--------------+---------+--------+--------+---------+-----------+-----------+-----------+-----------+--------+--
------+--------------
(0 rows)
conname | connamespace | contype | condeferrable | condeferred | convalidated | conrelid | contypid | conindid | confrelid | confupdtype | confdeltype |
confmatchtype | conislocal | coninhcount | connoinherit | consoft | conopt | conkey | confkey | conpfeqop | conppeqop | conffeqop | conexclop | conbin | c
onsrc | conincluding
omm=# \xExpanded display is on.
omm=#
omm=# select * from pg_constraint where conname like 'test_pkey';
(No rows)
omm=# alter table test add constraint test_pkey primary key(id);
NOTICE: ALTER TABLE / ADD PRIMARY KEY will create implicit index "test_pkey" for table "test"
ALTER TABLE
omm=# select * from pg_constraint where conname like 'test_pkey';
-[ RECORD 1 ]-+----------
conname | test_pkey
connamespace | 2200
conindid | 16395
confrelid | 0
confupdtype |
confdeltype | contype | p
condeferrable | f
condeferred | f
convalidated | t
conrelid | 16389
contypid | 0
coninhcount | 0
connoinherit | t
consoft | f
conopt | f
confmatchtype |
conislocal | tconkey | {1}
confkey |
conpfeqop |
conppeqop |
conffeqop |
conexclop |
conbin |
consrc |
conincluding |
omm=# \d test
Table "public.test"
Column | Type | Modifiers
--------+-----------------------+------------
id | bigint | not null
name | character varying(50) | not null
age | integer | default 20
Indexes:
"test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default
omm=# 
4.修改表字段的默认值
omm=# \d test
Table "public.test"
Column | Type | Modifiers
--------+-----------------------+------------
id | bigint | not null
name | character varying(50) | not null
age | integer | default 20
Indexes:
"test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default
omm=# alter table test alter column age set default 25;
ALTER TABLE
omm=# \d test
Table "public.test"
Column | Type | Modifiers
--------+-----------------------+------------
id | bigint | not null
name | character varying(50) | not null
age | integer | default 25
Indexes:
"test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default
omm=# 
5.修改表字段的数据类型
omm=# \d test
Table "public.test"
Column | Type | Modifiers
--------+-----------------------+------------
id | bigint | not null
name | character varying(50) | not null
age | integer | default 25
Indexes:
"test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default
omm=# alter table test ALTER COLUMN age TYPE bigint;
ALTER TABLE
omm=# \d test
Table "public.test"
Column | Type | Modifiers
--------+-----------------------+------------
id | bigint | not null
name | character varying(50) | not null
age | bigint | default 25
Indexes:
"test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default
omm=# 
6.修改表字段的名字
omm=# \d test
Table "public.test"
Column | Type | Modifiers
--------+-----------------------+------------
id | bigint | not null
name | character varying(50) | not null
age | bigint | default 25
Indexes:
"test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default
omm=# ALTER TABLE test RENAME COLUMN age TO stuage;
ALTER TABLE
omm=# \d test
Table "public.test"
Column | Type | Modifiers
--------+-----------------------+------------
id | bigint | not null
name | character varying(50) | not null
stuage | bigint | default 25
Indexes:
"test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default
omm=# 
7.修改表的名字
omm=# \d test
Table "public.test"
Column | Type | Modifiers
--------+-----------------------+------------
id | bigint | not null
name | character varying(50) | not null
stuage | bigint | default 25
Indexes:
"test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default
omm=# ALTER TABLE test RENAME TO mytest;
ALTER TABLE
omm=# \d mytest
Table "public.mytest"
Column | Type | Modifiers
--------+-----------------------+------------
id | bigint | not null
name | character varying(50) | not null
stuage | bigint | default 25
Indexes:
"test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default
omm=# 
8.删除表
--首先查看public模式下有哪些表，然后执行删除表操作omm=# SELECT table_name FROM information_schema.tables WHERE table_schema='public';
table_name
------------
mytest
(1 row)
omm=# drop table mytest;
DROP TABLE
omm=# SELECT table_name FROM information_schema.tables WHERE table_schema='public';
omm=# table_name
------------
(0 rows)
omm=# 
「喜欢这篇文章，您的关注和赞赏是给作者最好的鼓励」
关注作者
【版权声明】本文为墨天轮用户原创内容，转载时必须标注文章的来源（墨天轮），文章链接，文章作者等基本信息，否则作者和墨天轮有权追究责任。如果您发现墨天轮中有涉嫌抄袭或者侵权的内容，欢迎发送邮件至：contact@modb.pro进行举报，并提供相关证据，一经查实，墨天轮将立刻删除相关内容。
